Electron tube with replaceable filament



1963 R. A. SHORTRIDGE 3,114,063

ELECTRON TUBE WITH REPLACEABLE FILAMENT Filed Nov. 25. 1960 INVENTOR Robert A. Shortridge BY flwwilgff United States Patent 3,114,068 ELECTRGN TUBE WITH REPLACEABLE FILAMENT Robert A. Shortridge, Ashland, Ky. File-d Nov. 25, 196i Ser. No. 71,510 2 (Ilaims. (ill. 313-237) This invention relates to an electron tube and, in particular, relates to a replaceable cathode heater element for an electron tube.

It is well known that the failure of an electron tube, particularly a television tube, is most frequently occasioned by the burning out of the cathode heater filament. It has been suggested, as in Mcllvaine Patent No. 1,965,849, that the heater element could be made replaceable by using an electric lamp as the heating element.

The object of the instant invention is to produce an improved and practical means of constructing an electron tube with a replaceable heating element.

In general, this and other objects of the invention are accomplished as hereinafter described with reference to an equi-potential type cathode.

The cathode is separated into two parts, one part being contained within the neck of a television tube and having an electron emitting coating, while the other cathode part is a plug containing a heating element in a vacuum and removably attached to the first cathode part. Both parts have the same voltage applied to them so that they are of equal potential. When the heating element fails, the second part can be detached from the television tube and replaced by a new unit.

The means by which the objects of the invention are obtained are described more fully with respect to the accompanying drawing which is an exploded and cut-away perspective view of the neck portion and replaceable cathode plug portion of a television tube.

The television tube T has a neck portion containing the usual gun 12 held in place by spacer pins 14. The tube, including the neck, is composed of glass, and the neck has an integral bottom 16. Mounted in this bottom is a metal cylindrical cup 18 extending inwardly of the neck It The bottom 26 of the cup 18 has its surface which is exposed to the interior of the neck 10 coated with a layer 22 of electron emitting material, such as an oxide consisting of a metallic base of platinum, nickel, nickel alloyed with a small percent of cobalt or silicon, or an alloy consisting of nickel, cobalt, iron and titanium.

Cup 18 thus constitutes the first and permanent part of \a cathode. It remains sealed in the evacuated tube.

Cup 18 is enclosed by a cylindrical grid 24 having a circular aperture 26 in the center of its base 28.

The base of neck 14"] has a non-metallic socket 31 secured thereto, this socket being composed of glass, plastics, or ceramics. Socket pins 32 provide means for electrically energizing the grid 24 and the anodes in the gun 12.

The second md removable part of the cathode consists of a plug 40. This plug is composed of the metal cylinder 42 closed at each end and containing an electro-heating resistance wire 44. The center portion of tube 42 is surrounded by an insulating body 46 composed of glass or the like, this body being retained between two non-conductive shells 43 and 50. Body 46 has mounted therein socket pins 52 which provide means for electrically energizing the cylinder 42 and the heating element 44. The

3,l.l4,fih Patented Dec. 10, 1963 plug 44 is insertable into the socket 343 so that the upper end of the cylinder 42 extends into cup 18 and makes a snug contact therewith so as to be electrically coupled with cup 18. The plug can be fastened to the bottom of the neck 10 by any suitable means, such as by the bayonet joint 54.

The resistance element or filament 44 is composed of thoriated tungsten and coated with barium-strontium oxide or beryllium-aluminum oxide. Filament 44 is mounted in a vacuum within cylinder 42 and is heated to a temperature of approximately 1,000 K. Cylinder 42 and cup 18 are each made of a good heat conducting material, such as aluminum, or an aluminum alloy. Also cup 18 can have a tapered wall with the cylinder cornplementarily tapered so as to allow for heat expansion during operation and ease in mounting when plugged together.

When the second cathode part is coupled with the first cathode part, heat radiated from element 44 passes by conduction through cylinder 42 into cup 18 and thus heats emitting layer 22. As cylinder 42 is energized through pin 42a and is in metallic contact with cup 18, the first permanent cathode part consisting of cup 18 is at the same negative potential as cylinder 42 and operates at normal voltages from the zero to volt range. Although heating element 44 will necessarily operate at a little higher temperature than the conventional cathode filament due to some temperature loss through the connection between the two cathode parts, yet this is not objectionable. Should the heating element fail, then all that is necessary is to remove plug 40 and replace it by a new unit. Otherwise television tube T functions in the conventional manner.

Having now described the means by Which the objects of the invention are obtained,

I claim:

1. An electron picture tube comprising a tube having a neck portion including a neck bottom, a metal cylindrical cup projecting through said bottom into the interior of said neck portion, a coating of electron emitting material on the surface of said cup exposed to the interior of said neck portion and forming with said cup a permanent cathode for said tube, an apertured cylindrical control grid enclosing said cup within said neck portion, anode means mounted in said neck portion, a non-metallic socket secured to the free end of said neck portion, pin lead-in means secured to said socket for energizing said grid and anode means, respectively; a plug comprising a metal vacuum cylinder sealed at both ends, an electrical heating element mounted in said metal cylinder, said metal cylinder being removably positioned within and in electrical contact with said cylindrical cup for heating said cup by conduction, an insulating body surrounding said metal cylinder, electrical lead-in pin means extending into said insulating body for energizing said electrical heating element and said metal cylinder, respectively; and fastening means for removably securing said plug to said neck portion.

2. A television picture tube as in claim 1, said plug being snugly fittable Within said non-metallic socket.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AN ELECTRON PICTURE TUBE COMPRISING A TUBE HAVING A NECK PORTION INCLUDING A NECK BOTTOM, A METAL CYLINDRICAL CUP PROJECTING THROUGH SAID BOTTOM INTO THE INTERIOR OF SAID NECK PORTION, A COATING OF ELECTRON EMITTING MATERIAL ON THE SURFACE OF SAID CUP EXPOSED TO THE INTERIOR OF SAID NECK PORTION AND FORMING WITH SAID CUP A PERMANENT CATHODE FOR SAID TUBE, AN APERTURED CYLINDRICAL CONTROL GRID ENCLOSING SAID CUP WITHIN SAID NECK PORTION, ANODE MEANS MOUNTED IN SAID NECK PORTION, A NON-METALLIC SOCKET SECURED TO THE FREE END OF SAID NECK PORTION, PIN LEAD-IN MEANS SECURED TO SAID SOCKET FOR ENERGIZING SAID GRID AND ANODE MEANS, RESPECTIVELY; A PLUG COMPRISING A METAL VACUUM CYLINDER SEALED AT BOTH ENDS, AN ELECTRICAL HEATING ELEMENT MOUNTED IN SAID METAL CYLINDER, SAID METAL CYLINDER BEING REMOVABLY POSITIONED WITHIN AND IN ELECTRICAL CONTACT WITH SAID CYLINDRICAL CUP FOR HEATING SAID CUP BY CONDUCTION, AN INSULATING BODY SURROUNDING SAID METAL CYLINDER, ELECTRICAL LEAD-IN PIN MEANS EXTENDING INTO SAID INSULATING BODY FOR ENERGIZING SAID ELECTRICAL HEATING ELEMENT AND SAID METAL CYLINDER, RESPECTIVELY; AND FASTENING MEANS FOR REMOVABLY SECURING SAID PLUG TO SAID NECK PORTION. 